The new Third Generation Partnership Project (3GPP) standard known as Long Term Evolution (LTE) (3GPP LTE Rel-10) supports heterogeneous networks. In heterogeneous networks, a mixture of cells of different size and overlapping coverage areas are deployed. For example, a heterogeneous network may deploy Pico cells served by relatively low power nodes within the coverage area of a macro cell served by relatively high power base stations. Heterogeneous networks could also deploy relatively low-power home base stations and relays to provide improved service in indoor areas. The aim of deploying low power nodes, such as pica base stations, home base stations, and relays, within a macro cell where coverage is provided by a high power base station is to improve system capacity by means of cell splitting gains, as well as to provide users with wide area experience of very high speed data access throughout the network. Heterogeneous deployment schemes represent one alternative to deployment of denser networks of macro cells and are particularly effective to cover traffic hotspots, i.e., small geographical areas with high user densities served by lower power nodes.
In heterogeneous networks, there may be a large disparity in output power of the low power nodes compared to the base stations serving macro cells. For example, the output power of the base stations in the macro cells may be in the order of 46 dBm, while the output power of the low power nodes in the pico cells may be less than 30 dBm. In some heterogeneous networks, the macro cells and pica cells operate on the same carrier frequencies, and inter-cell interference coordination (ICIC) techniques are used to deal with interference when mobile terminals are operating in areas served by both macro cells and pico cells. For example, scheduling restrictions may be applied where a macro base station is prevented from transmitting in certain subframes, which may be referred to as “blank” subframes. The pico cells can use these blank subframes to transmit data to mobile terminals operating in a link imbalance zone near the cell edge of the pico cells without interference from the macro base stations.
Although scheduling restrictions may be applied by the base station to implement ICIC, there is currently no way to notify the mobile terminals about such scheduling restrictions. Thus, the mobile terminals must decode the Physical Downlink Control Channel (PDCCH) in all subframes, which may be unnecessary if scheduling restrictions apply to the mobile terminal. Also, because the received signals from the macro cell may be up to 10 dB stronger than the received signals from the pico cell, the mobile terminal might not be able to maintain synchronization with the pico cell and thus unable to decode the PDCCH transmitted by the pico cell. Another drawback is that there is currently no method to detect when a mobile terminal is in a link imbalance zone and thus should be subject to scheduling restrictions.